fix(studio): drain pending edits before reload (#2989)

* fix(studio): drain pending edits before reload

* fix(studio): address drain review feedback (#2989)

- prioritize conflicts and clear recovered DOM queue errors
- cover delayed blur effects and missing drain branches
- document stacked consumers and extend write-token retention

* test(studio): satisfy drain audit gate (#2989)

- share the editor-save hook harness across drain regressions
- extract settled failure inspection from the drain loop

packages/studio/src/utils/studioFileVersion.test.ts

@@ -1,5 +1,11 @@
 import { describe, expect, it } from "vitest";
-import { studioExpectedFileVersion, studioFileContentVersion } from "./studioFileVersion";
+import {
+  consumeStudioWriteToken,
+  markStudioWriteToken,
+  resetStudioWriteTokens,
+  studioExpectedFileVersion,
+  studioFileContentVersion,
+} from "./studioFileVersion";
 
 describe("studioFileContentVersion", () => {
   it("matches the strong SHA-256 ETag format used by studio-server", async () => {
@@ -34,3 +40,24 @@ describe("studioFileContentVersion", () => {
     expect(await studioExpectedFileVersion(versions, "untracked.html")).toBeUndefined();
   });
 });
+
+describe("studio write-token echo identity", () => {
+  it("suppresses exactly one matching API write receipt without hiding path-only external writes", () => {
+    resetStudioWriteTokens();
+    markStudioWriteToken("studio-write-1");
+
+    expect(consumeStudioWriteToken("studio-write-1")).toBe(true);
+    expect(consumeStudioWriteToken("studio-write-1")).toBe(false);
+    expect(consumeStudioWriteToken(null)).toBe(false);
+  });
+
+  it("keeps a token through a slow write and expires abandoned identity state", () => {
+    resetStudioWriteTokens();
+    markStudioWriteToken("slow-studio-write", 1_000);
+
+    expect(consumeStudioWriteToken("slow-studio-write", 61_000)).toBe(true);
+
+    markStudioWriteToken("abandoned-studio-write", 1_000);
+    expect(consumeStudioWriteToken("abandoned-studio-write", 301_000)).toBe(false);
+  });
+});